Calculate the pH of a solution at 25°C that contains 1 × 10⁻⁸ M of hydronium ions, i.e., H₃O⁺.
4.000
9.000
1.000
7.000
Correct answer: 7.000
Solution
The concentration of H₃O⁺ is very low (1 × 10⁻⁸ M), so the contribution of H₃O⁺ from water (10⁻⁷ M) must be considered. Adding these gives a total [H₃O⁺] of approximately 1.1 × 10⁻⁷ M, which corresponds to a pH close to 7.